1. Field of the Invention
The present invention relates to an optical transmitting module, particularly to an optical transmitting module having a CAN type package.
2. Related Prior Art
Recent optical communication system inevitably uses a semiconductor laser diode as an optical signal source because of its compactness and low power consumption. To drive the laser diode, bias and modulation currents must be adequately applied thereto depending on characteristics of the laser diode such as a threshold current and a slope-efficiency. These characteristics have large temperature dependence.
Moreover, recent optical communication system requests a high transmission speed over giga-bit rate, reaching 10 Gbit/sec. In order to realize such high transmission speed with a predetermined extinction ratio, enough current must be supplied to the laser diode, which results on an increasing of the power consumption, and accordingly needs a precise control of the current depending on the temperature of the laser diode
Therefore, a temperature sensor for sensing the temperature of the laser diode is necessary and installed within the package. In an optical transmitting module having, what is called, a butterfly type package, it is rather easy to build a thermoelectric device, typically a Peltier device, within the package because the butterfly type package has an enough space. By using the Peltier device, the temperature of the laser diode can be kept substantially constant. That is, a temperature sensor, such as thermistor, is installed immediate side of the laser diode on the Peltier device, and the temperature of the Peltier device can be controlled by a signal output from this thermistor.
On the other hand, in an optical transmitting module having, what we call, a CAN type package, it is quite hard to build the temperature sensor within the package because of its compact size. For example, an external diameter of the CAN type package is typically from 3.8 mm to 5.6 mm at most. The laser diode in the CAN type package is usually used without any temperature compensation.
Therefore, one object of the present invention is to provide an optical transmitting module capable of outputting a signal for controlling bias and modulation currents for the laser diode as varying the temperature thereof.